Dental casting flask



Aug. 16,1927.4 H. SPIRO 1,639,416

DENTAL: CASTING FLASH Filed Auz.28. 1926 mi /A A, /5 v i l Ivi Wy?? Patented Aug. 16, 1927.

UNITED STATES HARRY SPIRO, OF CHICAGO, ILLINOIS.

DENTAL CASTING FIJASK.

Application filedl August 2S, 1926. Serial No. 132,211;

This invention relates to improvements in casting flasks generally, and more especially to that type ofy flask frequently used in dental laboratories for the casting of 5 bridges, crowns, fillings, inlays, plates and the like.

In the practice of dentistry, the casting of gold', aluminum,l and other metalsV and 'alloys is aceomplished'byjthe preparation .l0 of molds-'for each individual cast, wherein aninvestment, such as plaster or other moldformingkmaterial, is placed in. va flask in plastic state, and a pattern having the form ofthe article to be produced' is embedded forced into the mold-space orcavity, and isl accomplished either by the use of anrapplication ofpressure to the top ofthe flask, or

a vacuum to the underside. Vhile I have here shownl the particular' embodiment of my invention as' adapted forv use in con-neef tion with the application of'pressure, it is to be understood that it is' equally well adapted for usewith suction. l ln cases where pressure 1sV used for'forcing the molten metal" into the mold-space or cavity, such pressure may' bel applied in a.

For example, a pressure v.lo machine may be used adaptedY to furnish air or other gas under pressure to the top ofy variety of ways;

the flask above the molten metal. Pressure alsoy may be applied byhand, by-covering the Y top of. the flask. with' several; sheets of wetl blotting paper held firmly in place. Byy

this method, steam is generated beneath the blotting paper furnishing pressure above the molten metal in the flask to force the metal downwardly into the mold-space or cavity.

When hardened, the investment is rather porous, and, in the use of a pressure machine, orif pressure is furnished by means of wet blotting paper, or in any other manner, the molten metal is forced downwardly through the sprue hole leadingI into the mold-space or cavity, under vthe action of'such pressure, the air in themold-space or cavity escapingVv into the pores of thel investment. In the use of a vacuum applied to the lower end of the flask, the action of the same draws thek air out of the mold-space through the pores in' the investment, with the result that the molten metal is forced into the mold-space 'or cavity under atmospheric pressure. A

In thehardening and: drying of the investment in the flask while setting, and alsov in theI heating of suchV investment for the purpose of driving` out its moisture content and renderii'ig it porous, suchl investmentshrinks toa certain extent. The heating of' the flask also causes a cert-aineXpa-nsion ofthe flask. SuchA resulting shrinking'v of theA investment andexpansifon of the flask causes a separation between the outery wall of they flask and' thel investment, leaving a crack or air space therebetween. One of the defects of many flasks as heretofore'made was the presence of such aA crack which permi-ttedV the escape of air therethrough, with either' theY pressure or vacuum system. @ne of thev features of my invention, is the provision of novel means for preventing such escape ofair. By the use of my invention, such escape around theA sides of the investment is prevented, and the pressure is directed to the region of the sprue hole and directly over themold.

My improved flask is also strong and durable, simple-and cheap to construct, and easy to operate. Other features and advantages of my invention will appear more fully as I proceedwith my specification.

In that forinof device embodying the features of myy invention shown in the accompanyingdrawings, Fig. l is ay vertical sectional view showing the casting flask inverted with the was; pattern in place in the l investment', and Fig. 2 is aA similar kview showing the flask right side up with the wax pattern and sprue wire removed, and molten metal poured into the investment.

As shown in the drawings, l() indicates a substantially cylindrical flask preferably having an outwardly turned flange ll at the bottom in order to give the same a steadier base. The upper edge of the cylindrical wall is bent inwardlyvand downwardly as indicated at l2, and its inner edge is bent downwardly to form the inner depending concen trical ring 13 lying inside of and parallel with the outer wall 1G of the flask.

ln the practice of the invention, the flask is inverted as shown in Fig. 1 on the top of a work bench or other suitable support (not shown) and is centered over a hopper or sprue wire support 14., which is circular in form and has a convex upper face provided with an opening at its center. The member 141 carries supported therein a sprue wire 15 upon the upper end of which is supported the wax pattern 16 of the object to be cast. rlhe flask is then filled with a suitable moldforming material or investment, such as plaster, 17, in the plastic state. After the investment has dried and set, the flask is turned right side up, and the member 14 ancL the sprue wire 15 removed.

Heat is then applied to the flask for the purpose of thoroughly drying the investment and driving all moisture therefrom, and for the destroying, melting, or vaporizing of the wax pattern 16.

After the investment 17 is thoroughlyT dried and preferably while the flask and investment are still in a heated condition, molten material such as, for example, molten gold 18 is poured in the conical top of the investment. lNhile the parts are still heated and the metal is still molten, pressure is applied to the upper end of the flask. This may be accomplished, for example, by means of an air pressure machine of any ordinary type. For example, 19 may indicate the pressure head of such a machine, which is adapted to engage with the upper edge of the flask, such upper edge being preferably ground, or a suitable gasket being provided, so that the pressure head will (2o-operate with the upper edge of the flask in a well known manner. rilhe application of the pressure forces the molten material 18 down into the mold cavity as indicated by 18a.

The particular feature of the invention is the provision of the inner ring 13, which prevents the escape of pressure from the top of the flask between the investment and the outer wall of the flask. As stated before, in the drying and heating of the investment and flask, the investment shrinks and the flask expands causing a crack between the investment and the outer wall of the flask, Such shrinking of the investment, however,

metal part 12, which obviously is also impervious to air. Consequently, if there is a tight joint between the outer side of theV inner ring 13 and the investment, no air can lea-k from under the pressure head out to the crack or space between the'investment and the outer wall 10. Y i

While I have shown and described certain embodiments of my invention, it is tor be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the Vappended claims, in which it is my intention to claim all novelty inherent in my invention as broadly as possible in view of the prior art.

lllhat l claim as new, and desire to secure by Letters Patent, is:

1'. An integrally formed dental casting flask comprising a cylindrical portion having a wide supporting flange at its base, and an inverted cone-shaped sprue-gate at its top terminating in a depending flange forming a short cylinder concentric with the aforesaid cylindrical portion and of relatively large diameter in relation to the sprue.

2. An integrally formed dental casting flask comprising a cylindrical portion hav ing an outwardly flared supporting flange at its base, and at its top, an inverted coneshaped sprue-gate which termina-tes in cylindrical apron concentric with the. afore`v said cylindrical portion, and formed by eX- tending the walls of the sprue-gate parallel with the axis of the llask to a considerable extent whereby the sprue-opening may be formed at a point above the lower edge ofA said apron.

ln testimony whereof, I have hereunto set my hand this 23rd day of August, A. D. 1926. HARRY SPIRO. 

